Variable inductance frequency modulation phonograph system



Apnl 5, 1949. R. BOUDREAUX 2,466,201

VARIABLE INDUCTANCE FREQUENCY MODULATION PHONOGRAPH SYSTEM Filed Dec. 11, 1944 3 Sheets-Sheet 1 By 2mm WWW Apnl 5, 1949. R. BOUDREAUX 2,466,201

VARIABLE INDUCTANCE FREQUENCY MODULATION PHONOGRAPH SYSTEM Filed Dec. 11, 1944 3 Sheets-Sheet 2 fiaierf fiaad re aaz B (ma Wu; 15! M 5 April 5, 1949. R. BOUDREAUX 2,466,201

VARIABLE INDUCTANCE FREQUENCY MODULATION PHONOGRAFH SYSTEM Filed Dec. 11, 1944 3 Sheets-Sheet 3 r E- M- "A'A'A A'A'A'A' lure/110)" urllrso snares VARIABLE INDUCTANCE CY MOD- ULA'LEQN PHQNUGRAPH SYSTEM Robert Boudreaux, Delcambre, La.

Application December 11, 1944, Serial No. 567,685

6 Claims. (Cl. 17'9l00.4)

This invention relates to the reproduction of in the received signal intensity between sounds phonographic records by means of electrical oscil of tone quality and sounds without such quality lations and it has for its primary object to use (noise) is much improved after the process of frequency modulated high frequency oscillations frequency modulation for this purpose. 5 It will be seen from the above that this imi It is a well known fact that reproduction of provement of the ratio between reproduction and phonographic records by means of electrical oscilnoise intensity which furnishes a much improved lations, although in many respects a vast imquality of the former is not dependent on anyprovement over the direct reproduction of the thing but the quality (including amplitude) of record, nevertheless does not eliminate he backthe generated sounds and it is, therefore, immaground of noises completely, this being due terial whether these sounds of undesirable qualmainly to the rhythmical character of the disity which ought to be eliminated originated durturbances, most of which are connected with the ing the recording or during the reproduction sweeping of the phonographic stylus or needle process. over the record surface. Disturbances of this The invention, tl'ereiore, relates to sound recharacter cause an irregular periodical or rhythproducing arrangements, in which sound repromical movement of the stylus or needle which duction by means of a stylus from a record is perare, therefore, able to influence or modulate formed by means of frequency modulated waves. the oscillation which is produced by means of the The invention consists in an improved arrangerecord. These disturbances, distortions and addimerit for producing frequency modulation in an tions on account of their character, which is inoscillation circuit operated by an oscillation furtimately associated with the principle on which nishing the carrier wave directly by means of a reproducing arrangement is based, cannot be the stylus moving over a record. eliminated completely. One of the objects of the invention is to pro- Part of the background of disturbing noise acvide an arrangeme t o t yp Which i5 companying a reproduction is moreover produced, ried by the tone arm and is contained within said due to causes which need not be explained her arm. While the receiver forming t t t during the making of the record by means of a of the arrangement in which the frequency modcutter and the usual type of reproduction arulated wave is s ject to du o pl rangement whose performance is geared to the floation, 6130., may be located anyw re a d p highest degree of absolute fidelity of reproduction era ly v at a i tan the fr q n y mod which is obtainable has clearly no means for lator should be closely associated with the tone eliminating disturbances of this kind. arm and form as comp ct and a sm ll a unit as Discrimination between disturbances without possible. This is not only necessary in order to tone quality (called hereinafter noise) and produce acommercially sound arr n Wi h musical or other well-defined tones is impossible a small and compact portable apparatus simiin the usual reproduction system in which the lar to the mechanical talking machines, but is stylus is caused to oscillate in accordance with also necessary on account of the short waves used the sinuosities of the sound track. All hitherto which can be shielded effectively against distu bknown filter arrangements interposed between the ances merely if all connections are short and if stylus nd the reproduction arrangement are all unwanted capacities, etc., are eliminated. suitable for this purpose as their activities are A further object of the invention consists in restricted to certain frequency bands. Systems, providing an arrangement in which the stylus which distinguish between tone of musical qualmay directly influence the frequency of a circuit ity to a certain extent and noises lacking this connected w the ll t r producing e quality, do, however, exist and these are the rier wave. frequency and phase modulation systems em- A number of still further objects and advanployed in radio transmission. tages gained by the instant system is described This modulation system permits a discriminamore fully in the following specification illustion between sounds of tone quality and other trating one modification of the invention. It is, sounds which are termed noise; the sounds of however, to be understood that the fact that tone quality of a given amplitude permit a shiftmerely one modification of the system is illusing of the carrier wave over a frequency range. trated is not to be interpreted in a limitative which is different from the range obtained by sense. Indeed, the invention relates to a new sounds without this quality and thus the ratio system of reproduction of phonographic records and the way in which the system may be embodied in actual phonographic apparatus is not limited to the single embodiment shown. To experts skilled in this art and in the art of radio transmission, it will be clear that, while using the presently described principles as a base, other embodiments may suggest themselves or may be developed without in the least departing from the essence or spirit of the invention described.

The invention is illustrated in the accompanying drawings in which Figure 1 is an elevational view partly in section of the tone arm of a phonographic reproduction apparatus (talking machine) showing the general arrangement of the parts.

Figure 2 is a plan or top view of the tone arm showing its curvature.

Figure 3 is a perspective view of the stylus and of the members and parts associated with it.

Figure 3a is an elevational cross sectional view, of the arrangement shown in Figure 3, the cross section being taken along the medium plane.

Figure 4 is a diagram of the connections of the parts or members forming the frequency modulation and the arrangement producing the frequency modulated wave.

Figure 5 is a diagram of the connections of a receiver or sound producing arrangement of the apparatus which is supposed to be arranged at a distance from the record containing part of the reproducing arrangement.

The sound reproduction method used according to the present invention consists in producing a carrier wave which is frequency modulated by the variation in electrical oscillations carried by the stylus; of a phonographic arrangement. The arrangement, when compared with the frequency modulation systems used in radio transmissions, is much simplified and reduced to the minimum of components; this simplification is rendered possible by the fact that frequency modulation is used here only for filtering purposes, and that, therefore, a great number of requirements supposed to be indispensable in radio transmission may be neglected. It may also be mentioned in this connection, that although short waves are used and are even indispensable, the arrangement is by no means confined to the narrow frequency band of ultra-short waves used for high frequency modulated radio transmission. Short waves of all kinds may be used, the selection depending mainly on the possibility to obtain the most compact and most simple arrangement which is not open to interference from outside.

The entire frequency modulation arrangement (which in the present arrangement includes the oscillator and all members and parts whose function it is to cooperate in the production of a frequency modulated wave) is arranged within a tone arm I, which is shaped approximately in the way in which the customary tone arms are shaped. It is slightly curved at one end 2 (Figure 2) which is hollow and accommodates the frequency modulator. At the other end a counterbalancing weight 3 is arranged, which is intended to balance the increased weight of the end 2 due to the inclusion of the modulator.

The tone arm I is carried by a tone arm support 4 which is pivoted to it by means of pivot bolts 5, which are journalled in rubber bearings 6. The support preferably rests on a ball bearing, designated in general by the reference numeral I. The support rests on the ball 8 of the bearing which is supported by a post 9 projecting from a base plate [0. The latter is firmly se- .between it and the core.

cured by means of a screw II in the customary box l2 carrying the arrangement.

The post is provided with indentations or cuts or with a groove l3 into which small set screws l4, attached to the support, enter. They prevent the support 4 and the tone arm I from being lifted or accidentally displaced.

The rear or stylus carrying part 2 of the tone arm usually termed cradle is provided with a slanting or slightly inclined bottom part I5, through which the needle I6 projects. This gives the needle a slight inclination which is supposed to be of a certain advantage when the stylus travels over the record.

The stylus 28 carrying the needle 16 may be of any approved type and it is here shown as consisting of a flattened cylindrical slitted member provided with the customary projections or shoulders l9. It may be fixed or supported according to any customary or approved method.

In order to mount the entire arrangement in the cradle, it is preferable, according to the invention, to use two L-shaped holding pieces l1. Ha, arranged transversely in the cradle between which the stylus 20 may be held. For this purpose, the frontal faces of the legs of the L-shaped holders are provided with cylindrical or halfmoon shaped recesses 23 of semi-circular cross sections accommodating the shoulders [9 of the stylus 243 over which rubber sleeves l8 have been slid.

It is to be understood that the way in which the stylus is attached is essential. Any well known stylus support may be used, its function being merely to hold the stylus in such a way that the oscillations of the needle are transmitted to the upper part of the stylus with the greatest fidelity and without introducing any distortion.

To the upper part of the stylus 20 a plunger or core 2! is fixed projecting into the interior of a coil 22. This plunger or core is fixed to the stylus by any known means, cementing or gluing being in this case preferable. The plunger or core 2| is a so-called dust core made of powdered steel or in order to provide extreme lightness of aluminum.

Behind the piston or core 2| a rubber damper 24 is arranged, a paper disc 25 being interposed The disc is made of very thin paper and its function is merely to prevent the rubber from sticking to the metal which frequently takes place during periods of rest when direct contact is made. The rubber damper 24 is mounted on a coil support 26, which is provided to hold the coil in its place. The coil support 26 itself is held by means of a projection or stem 21 which is secured in one of the L-shaped holders.

The coil 22 consists of a coil form 28 upon which the coil windings of coil 22 are wound. Around said coil a second coil form 30 with a coil 3| of a few windings only is arranged whose function will be explained later in connection with the diagram of connections.

On the other side of the stylus 20, another rubber damper 32 is arranged whose end face is covered with a paper disc 33. It serves to damp the free oscillations of the stylus 20.

As will be clear from the above description, the oscillations imparted to the needle and transmitted to the stylus will cause the latter to perform transversal oscillations which impart axial or longitudinal oscillations to the plunger or core within the coil. Thereby the inductance of the coil is varied in accordance with these oscillations. These variations of inductance are utilized in a way to be described.

As the stylus is rubber cushioned on both sides its free oscillations will be damped very effectively.

In order to be able to regulate the damping action the damping rubber pad 32 is mounted on a rod 34 whose position may be adjusted by means of a screw 35, which is held in the L-shaped sup port Ila. facing the support I1. Preferably the screw is buried within the hole 36 which is provided with the screw threads and after adjustment of the screw has been made during assembly or after testing the arrangement, the remainder of the hole 36 is filled with parafiin, or some other substance, in order to prevent adjustments by the user of the apparatus which would upset the correct damping.

The hollow end 2 of the tone arm i moreover contains all the components of the oscillatory circuit, viz: an oscillator tube 31 mounted on a socket 31a on which two or even three condensers (not shown in Figure 1) may be mounted. It moreover contains an adjustable condenser 38 (Figure 1), one plate of which is provided. with a pressure knob 39, projecting outwardly. By means of the knob 39 the capacity of the condenser may be adjusted, and this permits to adjust the frequency of the oscillations generated in the oscillator.

The coil of the oscillation circuit is the coil 22 whose location and mounting on the core in the cradle has already been described. As will be seen from the diagram shown in Figure 4, the oscillator tube 3'! forms part of the usual oscillation generator arrangement in whose grid and plate circuit the coil 22, the condenser 38 and the two condensers 39 and 48 are arranged. When the inductance of coil 22 varies by means of the core 2| penetrating into its interior to a varying extent, the inherent frequency of the circuit varies and the frequency of the oscillation which is then generated varies in proportion to the amplitude of the sound oscillations produced in the sound record. By means of the coil 3|, whose influence on the frequency is negligible and which surrounds coil 22, the frequency modulated oscillations generated in the oscillator tube are transmitted to an aerial or directly to a receiver.

An antenna may be used for various purposes. First, it is sometimes desirable to operate the sound producing speaker and the pickup at different places. Then, it is frequently desirable to keep the persons listening to the sound production away from a generator which is operated on the short wave band, as in spite of shielding, undesirable disturbances may be introduced by persons on account of their capacity with respect to ground. Finally, direct connections in this case are only preferable when certain precautionary measures are taken which are unnecessary in the event of transmission through the air.

If an aerial is used, a condenser 4|, shortening the effective length of the antenna, is preferably inserted.

The receiving arrangement containing the speaker which may be used in the event of a transmission through the air is shown in Figure 5, the arrangement being clearly about the same if direct transmission takes place, the coupling of the receiving circuit 42 with the aerial is then merely replaced by a coupling with the circuit containing the modulated oscillations. The circult connections shown in Figure 5 are purely conventional and need not be explained in detail as the diagram merely shows the customary type of receiver for frequency modulation. A heterodyne receiver generating an intermediate frequency may be employed, if desired. As will be clear to the expert skilled in this art, the oscillations are demodulated, detected in the detector 43 and after having been amplified are sent to the speaker 45.

From the above it will be seen that the construction of a phonographic apparatus in the form of a gramophcne, or the like, employin an electric pick-up and high frequency modulation is possible without radical changes in the mechanical construction. The difficulties arising out of the necessary use of very short waves are overcome partly by housing the entire transmitter or modulator arrangement in the tone arm thus avoiding conductors of substantial length and the introduction of feed back circuits by undesired capacitive or inductive couplings. Although. the receiver or arrangement connected with the speaker is more complex than the arrangement which has to be used in connection with the usual arrangement, this type of arrangement is merely a copy of the usual receiver which is a standard product and, therefore, does not cause manufacturing or other difficulties. The suppression of noise, however, may be carried to a degree which is unobtainable in ordinary arrangements even of the best quality and it may be further improved by using limitors and the usual arrangement for the suppression of the noise component, as used in connection with frequency or phase modulation.

The arrangement described may be used with phase modulation, the necessary changes being obvious to the experts skilled in the art.

What I claim is:

1. A frequency modulated sound reproduction arrangement with an electric pick up provided with a stylus, an oscillator, including an oscillator circuit and a receiving and reconverting arrangement for frequency modulated oscillations, comprising an inductance coil in the oscillation circuit, a transmission coil arranged concentrically to said inductance coil for transmitting oscillations tothe receiving and reconverting arrangement, both coils being arranged with their axis intersecting the axis of the stylus at right angles thereto, a movable metallic core, fixedly attached to the stylus and forming a unitary structure with the same, said core being arranged at right angles to the stylus and arranged to project into the space encircled by the coils.

2. A frequency modulated sound reproduction arrangement with an electric pick up provided with a stylus, an oscillator including an oscillator circuit and a receiving and reconverting arrangement for the frequency modulated oscillations, comprising an inductance coil, connected with said oscillation circuit and arranged at right angles to said stylus, said coil having a hollow interior, a cylindrical metallic plunger projecting into and axially movable within the hollow interior in the interior of the inductance coil, and attached to said stylus at right angles to the same, so as to form a unitary structure with it, damping means for said stylus projecting into the hollow interior of the coil and applied against said plunger and further damping means aligned with the aforesaid damping means and directly applied against the stylus.

3. A frequency modulated sound reproducer,

comprising a movable hollow tone arm, an eletric pick up mounted on said tone arm provided with a stylus, an oscillator including an oscillating circuit, mounted Within said tone arm, an adjusting condenser and an inductance coil in said circuit, the latter mounted with its axis at right angles to said stylus within said tone arm, a movable core for said inductance coil attached to said stylus, a receiving and reconverting arrangement outside of said tone arm and means to transmit the modulated oscillations produced in said oscillator and oscillator circuit to said receiving and reconverting arrangement including a coil concentric with said inductance coil.

4. A frequency modulated sound rcproducer, comprising a movable hollow tone arm, having an end portion inclined with respect to the remainder of the tone arm, frame members within said end portion, an electric pick up provided with a stylus mounted between the said frame members in the end portion of the tone arm, aligned resilient means for carrying said stylus between the frame members in said tone arm, an oscillator including an oscillator circuit, mounted in the hollow interior of the tone arm, an adjustable condenser within said circuit, having adjusting means projecting from said tone arm, an inductance coil with a hollow interior, arranged Within said oscillation circuit in the end portion of the tone arm close to the stylus, a movable metallic plunger forming a core for said inductance, attached to said stylus and project'- ing into the hollow interior of the same, and damping members for said stylus at right angles to the aligned resilient supporting means of the stylus on the frame members, and carried by said frame members, one of said damping members being adjustable with respect to said frame.

5. A sound reproducer for frequency modulated sound reproduction systems operated by the sound track of a phonographic record comprising a ton arm, an electric pickup provided with a stylus, an oscillator, including an oscillating circuit the latter including an inductance coil carried by said tone arm, frame members on said tone arm, means for carrying the stylus, arranged on said frame members, a metallic cylindrical plunger attached to said stylus, projecting substantially at right angles from the same, said plunger and said stylus forming a unitary structure, said inductance coil having a hollow interior and being arranged at right angles to said stylus, said plunger projecting into the interior of the aforesaid coil and forming a movable core for the same, damping means for said unitary structure arranged in the axis of the plunger including a non-metallic core member inside said coil, arranged coaxially with the plunger and attached to one of the frame members, a resilient cushioning member, carried by said non-metallic core and applied against the end face of the plunger, a further damping member arranged coaxially with the plunger and applied against the stylus and an adjustable supporting member for said clamping member carried by a further frame member.

3. A sound reproducer for frequency modulated sound reproduction systems, operated by the sound track of a phonographic record, comprising a tone arm, an electric pickup carried by said tone arm and provided with a needle support, an oscillator including an oscillator circuit, carried by said tone arm said oscillator circuit further including, an inductance coil arranged with its axis intersecting the axis of the needle support and arranged at right angle thereto, frame members associated with said tone arm, holding means for the needle support on said frame members and damping means associated with the same, arranged along a line intersecting the axis of the needle support and at right angles thereto and to the plane passing through the said axis and through the axis of the coil, and further damping means arranged along the last named axis of the coil for damping free axial movements along said axis.

ROBERT BOUDREAUX.

REFEREIJCES CITED The following references are of record in the file of this patent:

UNITED PATENTS Number Name Date 1,823,162 Pearson Sept, 15, 1931 2,210,303 Polydoroff Aug. 6, 1940 2,371,373 Badmaieff Mar. 13, 1943 2,436,946 Tatro Mar. 2, 1948 FOREIGN PATENTS Number Country Date 116,481 Australia l Jan. 20, 1943 OTHER REFERENCES Radio Craft, August 1941, page 90. 

